An estimated 60% of CA survivors are overweight/obese and sedentary. Observational studies have shown that lower BMI after diagnosis is associated with better breast and colorectal cancer survival. Clinical trials have yet to assess whether weight loss after diagnosis causes improved survival. Two substantial challenges exist to conducting large phase III studies of behavioral changes in cancer survivors: 1) rapid accrual of cancer patients who are geographically and socioeconomically diverse, and 2) access to an effective intervention that is transferable and sustainable in the real-world setting. The purpose of this proposed phase II pilot study is to assess the feasibility of conducting a weight loss intervention for breast and colorectal cancer survivors in the Southwest Oncology Group (SWOG). The study will use the Curves weight loss program, which combines circuit-based exercise with a high fruit/vegetable and low-fat calorie-reduced diet, and is widely available at over 5,000 Curves facilities across the US. Participants will receive an individualized weight loss goal and standardized support to reach their goal, including a 12-month membership to Curves fitness facility, a pedometer to track daily activity, and the Curves diet program via a manual and an on-line meal planning/dietary intake tracking program. The program will be supplemented with telephone behavioral counseling to increase education, intervention adherence and study retention. A total of 50 cancer survivors will be enrolled (25 breast and 25 colorectal cancer survivors) who are 6 months to 2 years post-treatment. Participants will be recruited using the rapid-accrual capabilities of SWOG. Minority cancer survivors will be targeted for recruitment at 26%. The primary aims of the study are 1) to determine the feasibility of a community-based combined physical activity and dietary change weight loss intervention in overweight and sedentary female breast and colorectal cancer survivors recruited via SWOG based on study accrual, intervention adherence, and study retention, and 2) to estimate the effect size of the intervention on weight loss. Secondary aims will assess changes in 1) anthropometric measures, 2) physical activity, 3) dietary patterns, 4) metabolic and hormonal biomarkers, and 5) quality of life, and will assess 6) the ability to enroll and retain a diverse patient population, and 7) the availability and acceptability of Curves. If this proposed intervention demonstrates feasibility and e5% weight loss, study results will be used to design a large phase III study to examine the effects of the Curves program on short- and long-term weight loss among overweight/obese female cancer survivors recruited via SWOG; secondary outcomes will examine the association between weight loss and disease-free survival. This study aligns with the mission of the NCI and the Office of Cancer Survivorship, which is to enhance the quality and length of survival of breast and colorectal cancer survivors.